MSXML XMLHTTP. MSXML 2.0 released with IE5 was first to support it. It got copied first by Mozilla, BTW, then as AJAX caught on in 2004 Safari copied it too.
Features that haven't been standardized are put in their own namespaces. For example, webkit-* and mozilla-* had conflicting implementations of CSS gradients for a while. After the standard was ratified, the prefix was removed. Safari still supported the old webkit-* syntax, and Firefox still didn't, just like before, but new pages could use the functionality without the prefix and it would work in both browsers.
Also, if webkit has settings or features that are specific to the library used, it makes sense to put those in a different namespace as well, to avoid pollution.
What is wrong with that? It's a vendor extension, like most new CSS and JS features are implemented. A draft specification for the Speech API exists since last October, if I'm not mistaken. So why would that not work?
And don't forget MIDI and Drect3D support was introduced in IE4. Before SVG, there was a trend of VRML in the industry and VML was added to IE.
And don't forget, the very first AJAX as made possible by the IE xmlhttp object.
TIME+dHTML was cool before Flash, even before these Web2.0 and HTML5 cool kids start yammering around.
And then Microsoft killed these features with their Silverlight.